The research proposed here focuses on electrophysiological correlates of the processing of learned, species-specific vocal signals by the avian auditory system. Vocal learning is a trait shared by man and many song birds. The role that auditory processing plays in the learning and perception of species-specific vocalizations will be examined using standard physiological techniques and synthetic vocalizations. Synthetic vocalizations will be generated along several acoustic dimensions suggested - from a wealth of ethological data - to be important in species and individual recognition. Computer averaged evoked brain potentials from surface electrodes and from depth electrodes in specific brain loci will be used to monitor electrical activity in the unanesthetized avian brain before, during, and after the sensitive period for song learning. Evoked potentials to tones and noise will be compared with evoked potentials to naturally-occurring vocalizations and to computer-synthesized variants encompassing these natural sounds. Evoked potential waveform analysis will involve standard peak and latency measures in addition to Principal Components Analysis and Multivariate Procedures in the search for electrophysiological correlates of auditory system plasticity, learning, and stimulus filtering in the processing of biologically relevant sounds. In addition, the EEG will be either zero-cross or spectrum-analyzed in an effort to assess the arousal potential of the critical stimuli involved in song learning.